Renewable biomass derived carbon material for metallurgical processes and method of making the same

ABSTRACT

A method for the production of a carbon material entirely from raw biomass feedstock for use in connection with a metallurgical production and refining process such as the production of steel, aluminum or silicon. The carbon material has a carbon content of greater than 50% by volume of non-volatile, high purity fixed elemental carbon and includes physical properties such as coking strength, conductivity, density, porosity, surface area and particle size which may be individually modified to meet the requirements of a specific metallurgical application.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/438,633, filed Dec. 23, 2016, which is incorporated herein by reference in its entirety as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to a novel composition of matter having application for use as an electrode, reducing agent, and carbon source in metallurgical processes and the method for its manufacture.

BACKGROUND OF THE INVENTION

Carbon serves an important role in the refining and manufacturing of several metals including aluminum, silicon, and carbon steel.

Aluminum metal is produced from aluminum oxide in the Hall-Héroult process, in which the aluminum oxide is electrolyzed in a molten mixture of cryolite with calcium fluoride. A consumable carbon anode serves the dual role of an electric current source for the process and a source of carbon to react with oxygen produced in the process to form carbon dioxide.

Silicon metal is produced in a similar fashion from silicon dioxide in an electric arc furnace using carbon electrodes. The carbon electrodes are oxidized by the oxygen in the silicon dioxide, reducing the silicon and leaving pure silicon metal.

In steel production, the carbon is utilized in the form of coke, which is burned as fuel and used as a reducing agent for the conversion of iron into steel. Coke is produced from metallurgical coals using a process which requires low levels of sulfur, phosphorous, and ash to prevent the addition of impurities in the coal to the coke product. Petroleum coke is a solid residue produced in oil refining which is resembles coke. However, it contains too many impurities to be useful in metallurgical manufacturing process.

Although only three examples are listed, carbon is used in a broad range of metallurgical applications including, but not limited to the production of titanium, zinc, copper, silver, gold, and many other applications. All of these applications utilize carbon as a fuel or reducing agent and produce CO₂ as a byproduct. If the carbon is derived from coal, or other fossil sources, the released CO₂ represents an increase in atmospheric CO₂ levels.

U.S. Pat. No. 3,215,522 A, “Silicon Metal Production” issued to August M. Kuhlmann on Nov. 2, 1965, describes a method of silicon metal production which uses electrodes made from coke, coal, and wood chips in an electric arc furnace. However, carbonaceous materials with fewer fines and low iron content are preferred over the materials disclosed by Kuhlmann.

US Patent Application Publication No. 20110150741 A1, published Jan. 23, 2011, now abandoned, by Lang et al. for “Production of Silicon by Reacting Silicon Oxide and Silicon Carbide, Optionally in the Presence of a Second Carbon Source” describes an improved method of silicon production utilizing a mixture of silicon oxide and silicon carbide with a secondary carbon source. The carbon source can include wood, or plant matter and charcoal, preferable low in boron and phosphorous.

U.S. Pat. No. 1,996,643 A, for “Improved Electrode and Method of Making Same” issued to De Pree, on Apr. 2, 1935, discloses a method for producing electrodes for a steel making process. In De Pree's process, carbon, graphite, or graphitized carbon are bound with rosin and oil to produce an electrode which will withstand oxidation at high temperatures.

Kuhlmann and Lang both focus on methods of silicon production and list preferred properties of carbonaceous electrode material. De Pree shows a method for producing resistant electrodes from a combination of a carbon material and pitch binders. None of the above patents describe a method for producing a carbon material with targeted properties for metallurgical processing; although, they do explain the properties of the used carbon being of significant importance. They also do not address a need for renewable materials or materials which have a negligible impact on atmospheric CO₂ levels.

In view of the foregoing, it is apparent that a need exists for a new and useful material which has properties similar to existing electrodes and cokes, but with targeted physical properties and which can be produced renewably and without the emission of fossil carbon dioxide or other pollutants into the environment.

SUMMARY OF THE INVENTION

The novel material and manufacturing processes herein described are complementary to the prior art and represent significant improvements thereto. In an embodiment, the present invention provides a method for the creation of a novel composition of carbon to be used in metallurgical processes through the pyrolysis of biomass particles under special treatment conditions to create specific properties targeted for use as a metallurgical carbon.

In another embodiment, a system is disclosed for carbon production which is integrated with the metallurgical process to provide increased efficiency and manufacturing costs reductions.

These and other advantages and novel features of the present invention will become apparent from the following description of the invention and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of a process for producing a carbon coke for steel production in which green biomass is first dehydrated and then introduced into a carbonization reactor where it is thermally decomposed into solid carbon coke and wood gas, useful as a fuel for biomass drying and for adding heat to a steelmaking process;

FIG. 2 is a flow diagram of a process for producing carbon electrodes for aluminum refining in which green biomass is first dehydrated and sized according to particle size and introduced into a carbonization reactor where it is thermally decomposed into solid carbon and wood gas, the solid carbon being used to form anodic and cathodic electrodes of an aluminum reduction cell; the wood gas being used as a fuel for biomass drying and steam production for process power generation; and

FIG. 3 is a flow diagram of a process for producing carbon electrodes for silicon refining in which green biomass is first dehydrated and sized according to particle size, introduced into a carbonization reactor where it is thermally decomposed into solid carbon and wood gas, the solid carbon being used to form electrodes of a silicon arc furnace and the wood gas being used as a fuel for biomass drying and steam production for process power generation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It should be noted that the present description is by way of instructional examples, and the concepts presented herein are not limited to use or application with any single method and/or apparatus for the production of a metallurgical carbon material. Hence, while the method of producing a novel carbon material of the present invention may be used in connection with a selected metallurgical precursor in the manufacturing of a preselected metal in a metallurgical refining unit such as a furnace. the details of the innovation described herein are for the convenience of illustration and explanation with respect to exemplary embodiments, and the principles disclosed may be applied to other types and applications of the production of metallurgical carbons from biomass feedstocks without departing from the scope hereof.

The Method:

Referring now to FIG. 1, by way of example and not of limitation, a flow diagram for a process 1 for the production of carbon coke which may be used in steel production illustrates the process steps of an exemplary embodiment of the present invention. Depending on the specific intended application, the novel final carbon product of the present invention, pre-processing of green biomass feedstock 10 may or may not be necessary. The pre-process step 12 includes the introduction or feeding of green biomass feedstock into pre-processing equipment which may include drying, sizing, and/or densification apparatus shown generally at block 14 to produce biomass feedstock 16 of a selected size and/or shape (for example, by pelletizing), moisture content and density. The sizing operation may be performed by chipping, cutting, screening, or similar processing to achieve the desired size for the metallurgical reaction, and the physical structure may be modified via chemical reaction, by way of example, by exposing the biomass to an acid, a base or another chemical agent adapted to modify the feedstock structure for the intended application.

Once the feedstock had been dried, sized, and otherwise prepared, at step 18, it is introduced to a carbonization reactor 20 where it is thermally decomposed or pyrolyzed at a sufficiently high temperature to drive off volatile carbon and create the high purity, highly fixed solid carbon structure or carbon coke 22. The carbonization or pyrolysis of the biomass at a preselected temperature of between approximately 350° C. and approximately 750° C. under atmospheric pressure for a preselected time of between one and twenty minutes will yield a carbon material which has a predetermined structure, size and density for the specific application. This structure may be created via any number of pyrolysis processes known in the art, including external heating, steam pyrolysis, or staged pyrolysis as described in Applicant's U.S. Pat. No. 9,505,984 B2 (the “'984 patent”). Any cost effective method for the carbonization would be suitable for this process. The carbon material may then be added directly to the steelmaking process at step 23 or processed further as will be discussed in greater detail below.

By way of example and not of limitation, the pyrolysis process as described in the '984 patent, produces the desired carbonized structure without the need for external fuel beyond the chemical energy in the biomass feedstock. Additional carbonization by-products such as wood gas 24 are also produced in the pyrolysis process which may have a number of uses, all of which create significant economic advantages and enhanced efficiencies over prior art systems and manufacturing processes.

First, it reduces operating costs since the wood gas may be directed to a combustor 26 as shown at step 28 where it is burned for heat recovery, producing hot gas for biomass drying 30, step 32, a portion of which may be directed to a blast furnace 34 at step 36 for adding heat to the steelmaking process. The need for fuel from extraneous fuel sources, which would otherwise be required to be burned for process heating, is eliminated. Moreover, the excess wood gas produced by carbonization, which does not drive the carbonization process, can be used to produce steam and/or electricity to offset the electrical needs of many metallurgical production and refining processes, to provide heat for biomass drying, and/or to fire a furnace. Hence, a synergistic integration of carbonization and electricity production with a metal refining facility is created.

Second, a substantial environmental benefit is realized by not utilizing fossil carbons for fuel or feedstock in metallurgical processing. No fossil CO₂ emissions from the reduction reaction are present; the emissions being substantially if not completely free of any environmentally hazardous compounds or chemicals. Moreover, other heat and/or electrical requirements can be offset using produced wood gas, as noted above.

Referring again to FIG. 1, once a carbon with the desired properties and dimensions has been created, it may be densified or agglomerated into a larger electrode. Otherwise the produced carbon can be used directly in the refining process of iron ore 36 (Fe₂O₃ and Fe₃O₄), as an electrode, fuel, or strictly as a reducing agent creating pig iron 38 and carbon dioxide gas 40 as depicted at step 42. Carbons described herein can also be used as a re-carburizing carbon to adjust to total carbon content in steel.

FIG. 2 is a process flow diagram of a process 50 for producing carbon electrodes for use in aluminum refining in accordance with an embodiment of the present invention. As described above with respect to the process for making carbon electrodes for steel making applications and in a similar manner, green biomass 52 may be introduced via step 54 to preprocessing equipment apparatus shown generally at block 56 to produce biomass feedstock 58 of a selected size, moisture content and density.

The dried and sized biomass 58 is introduced via step 60 to a carbonization reactor 62 where it is decomposed at high temperature (between approximately 350° C. and approximately 750° C.) under atmospheric temperature into solid carbon 64 and wood gas 66. The wood gas may be directed to a combustor 68 as shown at step 70 where it is burned for heat recovery, producing hot gas for biomass drying 72, step 74. A portion of the wood gas produced during the carbonization process may also be used to produce steam 76 at step 78 which is directed to an electrical power generator 80 to provide electricity for the aluminum making process at step 84.

The solid carbon 64 produced in the carbonization process at 62 is then introduced into an electrode forming apparatus 86 where it is mixed with a binding material and formed into one or more solid electrodes 90. The electrodes are installed in an aluminum reduction cell at step 94 to provide a reducing agent and an electron sink to process alumina 96 (A1 ₂O₃) into molten aluminum 98 and carbon dioxide 99 at steps 100 and 101, respectively.

FIG. 3 is a process flow diagram of a process 110 for producing carbon electrodes for use in silicon refining in accordance with another embodiment of the present invention. As described above with respect to the processes for making carbon electrodes for steel and aluminum making applications and in a similar manner, green biomass 112 may be introduced via step 114 to preprocessing equipment apparatus shown generally at block 116 to produce biomass feedstock 118 of a selected size, moisture content and density.

The dried and sized biomass 118 is introduced via step 120 to a carbonization reactor 122 where it is decomposed at high temperature (between approximately 350° C. and approximately 750° C.) under atmospheric temperature into solid carbon as above which is formed into carbon electrodes 124. Wood gas 126 is a by-product of the carbonization process which may be directed to a combustor 128 as shown at step 130 where it is burned for heat recovery, producing hot gas for biomass drying 132, step 134. A portion of the wood gas produced during the carbonization process may also be used to produce steam 136 at step 138 which is directed to an electrical power generator 140 to provide electricity 141 for the silicon making process at step 142.

One or more of the electrodes 124 formed of the carbon are installed in a silicon arc furnace 144 at step 146 to provide a reducing agent and an electron sink to process silica 148 into molten silicon 150, at step 152 and carbon monoxide 154 and carbon dioxide 156 at step 158.

The Product:

The end product material of the manufacturing processes described above with respect to the embodiments of the processes of the present invention possesses a number of properties and characteristics which overcome the shortcomings of the prior art and make it ideal for use as a metallurgical processing or refining material, a reducing agent, and as a source of metallurgical carbon. The material may be formed into an electrode by incorporating a binder and by submitting the material to a densification process. The material's properties and characteristics include by way of example:

1. a composition of matter, particulate or pelletized material created entirely through the pyrolysis of biomass which has greater than 50% by mass of non-volatile, high purity fixed elemental carbon, the composition of which material may be adjusted for a specific metallurgical application;

2. a sulfur content less than or equal to approximately 1% by mass;

3. an ash content less than or equal to approximately 10% by mass;

4. a content of less than approximately 10 mg/kg of each of the following: antimony, arsenic, barium, cadmium, chromium, cobalt, copper, lead, nickel, mercury phosphorous, boron and selenium;

5. a content of less than approximately 5 μg/kg of any polycyclic aromatic compound;

6. a surface area of between approximately 10 m²/g to approximately 600 m²/g as measured by nitrogen absorption techniques.

7. substantially free of any environmentally hazardous chemicals or components; and

8. the following physical properties which may be adjusted to meet the requirements of a specific metallurgical application, including but not limited to, coking strength, conductivity, density, porosity, surface area and particle size.

Changes may be made to the foregoing methods, devices and systems without departing from the scope of the present invention. It should be noted that the matter contained in the above description should be interpreted as illustrative and not in a limiting sense. The following claim(s) are intended to cover all generic and specific features described herein as well as statement of the scope of the present invention, which, as a matter of language, might be said to fall therebetween. 

What is claimed is:
 1. A method for the production of a carbon material from raw biomass feedstock for use in connection with a metallurgical production and refining process, the method comprising: introducing raw biomass feedstock to a carbonization reactor; carbonizing the biomass feedstock at a preselected temperature at atmospheric pressure for a preselected period of time, thereby creating a carbon material having predetermined carbonized structure, properties and dimensions and carbonization by-products; introducing the carbon material and a metallurgical precursor into a metallurgical refining unit; heating the carbon material and metallurgical precursor to produce a preselected metal.
 2. The method of claim 1 further including preprocessing the biomass feedstock prior to carbonizing it.
 3. The method of claim 2 wherein preprocessing the biomass feedstock includes drying the biomass feedstock to a preselected moisture content.
 4. The method of claim 2 wherein preprocessing the feedstock includes densifying the feedstock and forming or sizing it into a preselected size and/or shape.
 5. The method of claim 2 wherein preprocessing the biomass feedstock includes chemical modification of the biomass feedstock through exposure to an acid, a base or another chemical agent adapted to modify the biomass feedstock's physical structure.
 6. The method of claim 1 including processing the carbonization by-products to provide fuel for the generation of heat, steam, electricity or other energy for biomass feedstock processing.
 7. The method of claim 6 wherein processing the carbonization by-products further includes utilizing a portion of the carbonization by-products to generate heat, steam, electricity or other energy for the metallurgical production and refining process.
 8. The method of claim 1 wherein the metallurgical precursor comprises iron ore and wherein the preselected metal end product comprises iron.
 9. The method of claim 1 including introducing the carbon material having a predetermined carbonized structure into an electrode forming apparatus, mixing the carbon material with a binding material and forming the mixed carbon and binding material into one or more carbon electrodes.
 10. The method of claim 9 including installing the one or more carbon electrodes in a metallurgical refining unit.
 11. The method of claim 10 wherein the metallurgical precursor comprises alumina and wherein the preselected metal end product comprises aluminum.
 12. The method of claim 1 wherein the metallurgical precursor comprises silica and wherein the preselected metal end product comprises silicon.
 13. A metallurgical processing and refining material comprising greater than 50% by volume of non-volatile, high purity fixed elemental carbon.
 14. The metallurgical processing and refining material of claim 13 further comprising a sulfur content of less than or equal to approximately 1% by mass.
 15. The metallurgical processing and refining material of claim 14 further comprising an ash content of less than or equal to approximately 10% by mass.
 16. The metallurgical processing and refining material of claim 15 further comprising less than or equal to approximately 10 mg/kg of each of the following components: antimony, arsenic, barium, cadmium, chromium, cobalt, copper, lead, nickel, mercury, phosphorous, boron and selenium.
 17. The metallurgical processing and refining material of claim 16 having a surface are of between approximately 10 m²/g to approximately 600 m²/g.
 18. The metallurgical processing and refining material of claim 17 which is substantially free of environmental hazardous chemicals or components.
 19. The metallurgical processing and refining material of claim 18 wherein the material is produced entirely from raw biomass feedstock.
 20. The metallurgical processing and refining material of claim 19 further including the following physical properties which may be individually modified or adjusted to meet the requirements of a specific metallurgical application: coking strength, conductivity, density, porosity, surface area and particle size. 